Ignition system



Nov. 17, 1942. J. BERNARD 2,302,364

I IGNITIONSYSTEM Filed April 16, 1938 at v Patented New. rr, ra a HGNHIUN SYSTEM .lean Bernard, Paris, France Application April 16, 1938, Serial No. 202,571 in France March 10, 1936 Claims.

The present application forms a continuationin-part application of my co-pending application Serial No. 97,299, filed August 21, 1936.

The present invention relates to the distributors of ignition rna-gnetos for multi-cylinder engines, such for example as the present engines with 12, 14, 18 cylinders, etc., in star, V or W formation, and, in general manner, for ,all engines having radial cylinders and pistons connected to the crankshaft through the instrumentality of a main connecting rod and of secondary connecting rods coupled to said main connecting rod.

The construction of magneto distributors for this kind of engines lead to considerable diameters and weights, in particular in the case of aircraft engines which are required to-operate at high altitude, for example above 6000 meters, and when it is not desired to have recourseto a hermetic casing for the magneto and to artificially re-establishing the pressure at ground level within said casing.

The object of the invention is to provide distributors having a weight and a bulk less than the distributors heretofore known while providing for an equal safety of the ignition at a given altitude, or, for a given weight and bulk of the distributor, to increase the maximum altitude at which the distributor will operat with an equal safety.

Another object of the invention is to space the studs of the distributor so as to further the formation of the spark.

With these and other aims in view, the invention essentially consists in a distributor the studs of which are so spaced apart that the spacing angle between any two successive studs is not equal as usual to the geometrical spacing angle on the firing diagram between the axis of those engine cylinders which carry spark plugs respectively connected to said studs, but equal to the aforesaid geometrical spacing angle or to a fraction thereof plus or less a minute angle the value of which is chosen in dependence on the relative displacement of the dead centre position of the pistons in said cylinders at the time of the ignition.

By relative displacement of the dead points, I wish it to be understood the small angle through which the crankshaft must rotate in addition or in subtraction to the geometrical spacing angle between the axis of any cylinder considered and the cylinder aXis of the piston directly connected to the crankshaft through the main connecting rod, or to a fraction of said angle, to bring to its dead point position in the cylinder considered the corresponding piston which is connected to the main rod by a secondary rod, as is well known in the art; usually this small angle is not the same for all the pistons.

The invention will now be described as applied to a distributor of magneto designed to supply a given engine'having fourteen cylinders in double star-formation.

In the accompanying drawing:

Fig. 1 is a partial diagram showing two various manners of spacing the studs of the distributor, and Figs. 2 and 3 are diagrams showing the results obtained in each case.

Fig. 4 diagrammatically illustrates a distributor of magneto.

As is well known, the distributor includes a stationary body i5 made of insulating material in which are embedded studs l6 conveniently spaced apart to form a circular row and adapted to be respectively connected to the spark plugs of the engine to be ignited. In the present instance, there are fourteen studs which are to be respectively connected to the fourteen spark plugs of the engine. Said studs cooperate in the usual manner with the rotary distributing arm l'l carried by a shaft adapted to be connected to the engine crankshaft to be driven thereby at half the speed of the engine.

In 'the engine in question, the shafting for each star is of the usual type including a main connecting rod directly connecting the crankshaft to one piston and six secondary connecting rods which respectively connect the other pistons to said main connecting rod. It is a known fact that with such a shafting the crankshaft must rotate through successive various angles to successively bring the various pistons to their respective dead centre position. For the proper understanding of the invention, one of the two cylinders containing a piston directly connected to the crankshaft through the main connecting rod will be called cylinder I, and the successively ignited cylinders will be called cylinders 2, 3 It according to the order of ignition and each stud of the distributor will bear the same reference numeral l, 2 It as the cylinder to the spark plug of which it is to be connected. While in the present instance, the geometrical spacing angle between the cylinder axes is constant and substantially equal to 2543, the crankshaft must rotate through the following different angles, when starting from cylinder I, to successively bring the various pistons of cylinders 2 I to their dead point position: 52 20', 54 32', 50",

46 16', 50, 54 32', 52 20', 54 32'. and so on. There is thus a forward relative displacement of 54 of the dead centre position in cylinder 2, a forward relative displacement of 4 of the dead centre position in cylinder 3, a rearward relative displacement of 236 in cylinder 5 and so A first manner of angularly spacing the studs in accordance with the invention is diagrammatically shown in Fig. 1 on the circle 11 and the results obtained. are illustrated in Figs. 2 and 3.

In the disposition shown in this circle II, the angle between the studs l6 and I6 corresponding respectively to the cylinders I and 2 is equal to 26 10', i. e., to half the angle through which the crankshaft must rotate from its position where the piston is at its dead point position in cylinder 1 to bring the piston in cylinder 2 to its dead point position, i. e., the ignition position, if account is not taken of the advance of the spark. Similarly, the angle between any two studs is equal to half the angle through which the crankshaft must rotate between the ignition in two successively ignited cylinders. As the rotary arm I! which is connected to the crankshaft and rotates at half the speed thereof is arranged to be in contact with the stud corresponding to the cylinder to be ignited, at the instant where the spark is initiated by the means of an interrupting cam, which is correspondingly shaped. These instants being indicated on Fig. l by the radii 01, 02 it is clear that its position relatively to the stud engaged is always the same at this instant whatever -is the stud considered. In other words, the angle a (Fig. 1) formed at the said instant between the radius passing through the middle of the stud and the radius passing through the rear edge of the rotary arm H at the same instant is constant for all the studs since the radii indicating the ignition instants determined by the interrupting cam are in this case superposed to the radii passing through the middle of the studs, and therefore the duration of the engagement between the rotary arm and a stud after the spark has been initiated in the corresponding cylinder is constant for all the studs. On the other hand, the leakage angle, i. e., the angle ,3 between a radius passing through the rear edge of the rotary arm and the edge of the rearwardly situated stud at the instant where the spark is initiated by the said interrupting cam varies from one stud to the other. The successive values of a and [3 in this arrangement for the successive studs l, 2 M are shown respectively by the lines II on Figs. 2 and 3, and the minimum value of a and ,3 has been called mm B'id flin- It will be appreciated that this minimum value firn is greater by about 12% than the corresponding minimum value in the usual arrangement shown on the circle I of Fig. 1 where the spacing angle between two successive studs is constant and equal to 43' while the. minimum value an: of a is the same in both cases.

Accordingly the minimum leakage arc corresponding to flm is increased by about 12% over the minimum leakage arc of arrangement I for the same diameter of the distributor, i. e., the distributor may operate with equal safety at a higher altitude, or the diameter may be substantially reduced without reducing the safety of operation of the distributor at a given altitude.

An other advantageous arrangement of the studs is shown on the circle III of Fig. 1. In this arrangement, each stud is shifted with reference to its usual position by an amount equal to half the relative displacement of the dead point of the piston working in the cylinder associated to the next following stud. Since this relative displacement amounts to 54 for the piston working in the cylinder 2, the stud lfial associated to the cylinder I ignited immediately before cylinder 2 will be disposed with its middle point situated on a radius forming an angle equal to 27' with the radius representing the axis of the cylinder 0n the ignition diagram shown in Fig. 1 and the other studs will be positioned in the same way.

The results obtained with such an arrangement are shown by the lines III in Diagrams 2 and 3. It will be seen that the leakage angle [3 is constant while the contact angle a is variable. Assuming that the rotary arm is given such a length that the contact angle a will be the same as the minimum contact angle am with the usual arrangement shown on the circle I, it will be found that the smallest leakage arc pm is improved by about 12% over the minimum leakage arc [3m of the usual arrangement. Th results as regards bulk and weight are the same as with the arrangement II.

As regards reduction of bulk and weight, the arrangements II and III are therefore equal but the arrangement II is more interesting when the magneto is to be used at high altitude since when the minimum leakage path becomes insufficient and the spark consequently occurs between the rear of the rotary arm and the stud which has just been passed over, that is to say the stud of the cylinder already ignited immediately before, a single cylinder out or seven misflres and it is necessary to go much higher for there to be no ignition in a second cylinder. With the arrangement III, the ignition ceases simultaneously in all the cylinders and the engine stops dead. Furthermore in the arrangement II the rotary arm may be of much smaller length than in cases I and III. thereby facilitating the ignition when starting. The two above mentioned arrangements have only been given by way of example. Each stud can also be corrected individually so as to obtain a distributor in which on the one hand the contact are and on the other hand the leakage are are improved on the studs which are most unfavourable from this point of view in an uncorrected distributor. Without increasing the dimensions of the distributor it is thus possible to improve the ignition of the cylinders having contact arcs which are too small and to increase the altitude at which the first misfire will occur in equally spaced apart in a row and in which the spacing angle between any two successive studs is not equal to the geometrical spacing angle, on the firing diagram of said engine, between the lines representing the axes of those cylinders provided with spark plugs respectively connected to said studs, but to the aforesaid geometrical angle corrected by a minute angle the value of which is chosen in dependence on the relative displacement of the dead centre position of the pistons in said cylinders at the time of ignition.

2. In an ignition magneto, a distributor as in claim 1, wherein each stud is angularly spaced apart from its usual, non corrected position, by an amount equal to half said relative displacement of the piston Working in the cylinder which carries the spark plug to be connected to said stud.

3. In an ignition magneto, a distributor as inclaim' 1, wherein each stud is angularly spaced apart from its usual, non corrected position, by an amount equal to half the relative displacement of the piston working in the cylinder which carries the spark plug to be connected to the next following stud.

4. In an ignition magneto, a distributor as in claim 1, wherein at least one stud is'angularly spaced apart from its usual, non corrected position, by an amount equal to' at least a fraction of half said relative displacement of the piston working in the cylinder which carries the spark plug to be connected to said stud, and. at least one other stud is angularly spaced apart from its usual, non corrected position, by an amount equal to at least a fraction of half the relative displacement of the piston working' in the cylinder which carries the spark plug to be connected to the next following stud.

' having non symmetrical firing intervals due to the-arrangement ,of said (secondary connecting 5. In an ignition system for internal combustion engines of the radial cylinders type pr0' Q vided with a'master connecting rod and with,

secondary connecting rods pivoted thereto and rods, an interrupting cam shaped to initiate the ignition sparks substantially at the same period of the cycle in each cylinder and a distributor having studs unequally spaced apart in a row two; successivestuds s equal to the geometrical j I angle between the lines representing the axes! of the cylinders corrected by a minuteang'le the value of which is chosen in dependence oi" and in which the spacingangle between any 

